I used Eco-Complete in my 180 gallon tank and it looks great at first.
The black color is really a nice contrast in the tank. Over time though
you begin to notice that there are white or gray rocks of various size
in there as well. Has no bearing on anything other than aesthetics.

As for how effective it is, it's hard for me to say. My Ludwigia's are
growing out of control, but my sword plants have never really taken
off. It's either that there's not enough iron or not enough light (I am
guessing it's probably not enough light in my tank).

I was actually thinking of going with a custom mix next time of
flourite red, peat moss, and a thin top layer of black sand...but
that's still some ways off.